Plant basic biology-1 { Roots and rhizomes}

How many gardeners have become frustrated by attempts to pull up a dandelion from their lawn or from cracks between paving stones or on a drive way, only to find them reappearing after a few days ?

In many of the pages on this site I have introduced several wild flowers and some garden flowers, hopefully passing on some knowledge of them, including their uses and how to identify them.

In this series of pages I will share my knowledge of how plants live and thrive, starting with the root system. It is my intention to keep the text as simple as possible in the hope it will be more interesting and not bogged down in technical jargon or botanical terminology.

Root systems of Prairie plants.

What is a root ?

Upon germination of the seed the embryo root, termed as a radicle, grows and develops into the first true root. This first root may grow on to develop into a tap root with many branching lateral roots, or it may develop into adventitious roots. It may also develop into fibrous roots which are very fine and completely opposite to the tap root.

There are aerial roots that grow above the ground. Tuberous roots that are thick and relatively soft, with storage facilities, typically thick and roundish in form such as the potato. There are corms, bulbs, rhizomes,and stolons to name a few types of root system.

The first under review is the tap root, referring back to the opening paragraph,the frustration is due to the dandelion having such a root system. Tap roots grow straight down vertically an organism from which other lateral roots grow out into the soil. One of the main sources of the gardeners frustration is the ability of a damaged tap root to regenerate itself at the point where they have broken off. Away from our neatly manicured lawns and pristine driveways it is the natural way for the species to survive.

They are typically wide at the top tapering at the bottom as in the dandelion, others are known as fusiform, this type being widest at the middle and tapering at the top and the bottom. Another form is like the shape of a spinning top, wide at the top then suddenly tapering at the bottom, an example of this "Napiform" is the turnip.

Many plants have tap roots these include Burdock and goat'sbeard and garden vegetables such as parsnip and carrot. Of course many of the tap roots are edible as the last two named suggests. Nearly all species od seed plants begin their life with a tap root. However, most tap roots die off or the growth is diminished and replaced by spreading lateral roots that stretch out into the soil.

Below--Primary and secondary roots.

Rhizomes-----

Rhizomes are thick, mainly underground, structures, of familiar plants such as mint and iris, whose buds develop into new growth. The word rhizome derives from the Greek rhiza meaning a root or rhizoma indicating a mass of roots. They are often referred to as rootstock, or creeping rootstock.

In general rhizomes have short internodes {the part between the nodes}. They generate new shoots from the roots. Roots form from the nodes and while shoots arise from the top, thus vegetative reproduction begins. Some species have rhizome that appears just above the soil, species such as Geum, Iris and many ferns.

As with the tap root any part of the rhizome that has been left in the ground will regenerate new growth. Thus plants that are not wanted in the garden or allotment, such as the rosebay willow herb, the whole rhizome must be dug out to prevent vegetative regeneration.

Below---Geum have rhizomes

photograph by Dal

How do roots work ?

The root is the main organism that takes up water and liquid nutrients { for example plant food} from the soil that sustains most seed plants and ferns. It is also capable of storing reserves. The root has another important function, that of anchoring the plant into its growing medium, ie, soil, clay, compost etc.

As we have seen most roots grow below ground level and is, therefore, an extension of the above ground growth. Roots also help to prevent soil erosion. A root has three layers which are as follows----

The Epidermis--from the Greek epi-meaning upon , above or over, + derma meaning skin. It is the outermost layer and acts as a protective covering. It sometimes referred to as the cuticle.

CORTEX---This layer is a practical storage area for food and water, air spaces and the endodermis { from the Greek endo, meaning within + dermis meaning skin} The endo dermis is the inner boundary of the cortex which controls the passage of water and liquid nutrients.

Vascular Area---is the inner most area of the root contains vascular tissue which is composed of two types of cells, Xylem cells and Phloem cells. Xylem cells { from the Greek xulon meaning wood} transports the water and other liquid nutrients to the stems and other parts of the plant. Phloem { from the Greek phloos, meaning bark} cells carry food from the stem to the root.

The pericycle is a single layer of cells surrounding the vascular tissue. Branch roots grow from the pericycle.

Below-- Bugle spreads by means of Stolons

photograph by Dal

Below----Rosebay willowherb has rhizomes

photograph by Dal

Many plants have----

Many plants such as strawberries, creeping buttercup, and bugle have stolons or runners, which spread along the soil away from the parent plant. These stolons are capable of rooting themselves at intervals along their length. Once rooted new growth occurs and it is efficient means of establishing new growth away from the parent plant.

In the case of the creeping buttercup it can cause some consternation has it spreads by this means across manicured lawns.In the case of the bugle and others of its ilk it is an excellent ground cover species that allows large areas to become covered by its beautiful spikes from just a few plants being originally planted.

RELATED PAGES---Plant Basic Biology--2 FOLIAGE AND THEIR FUNCTION.

Plant biology -3 foliage continued

Plant biology-4 flowers

Other flora that feature on this site may be viewed by clicking on the individual banners { they are all grouped together.

Reuse of images

The images on this page may be reused. However, the name of the relevant author must be attributed along with any accompanying license.